Lets make sure we are all talking about the same thing here. the original poster was talking about "Classic Production Supercharged" and somewhere in the thread it got changed to C/PS which is C engine, Production Supercharged (C/PS). There were very few classic production supercharged vehicles ever available.
Production Supercharged does allow turbochargers if the production vehicle being entered originally came with a turbocharger. Like J.D. said, it has to be like for like but it can be much bigger. You CANT replace a screw type S/C with a turbo and call it production supercharged but you CAN replace a T25 turbo with a GT60 and remain in production supercharged.
On production vehicles the general rule is that it has to appear aerodynamically and visually stock (externally) and since the turbo is external on a M/C you pretty much have to keep the stock unit where on a car it's under the hood and not external so you can change it. At least thats how I always understood it.